Modern super high resolution 4K digital cinema projectors designed for normal sized cinema screens have a resolution ideal also for very large screens but lack the brightness needed for these. Double stacking projectors are an effective way of increasing brightness, but traditional double stacking is difficult at such high resolutions because the tolerance in the alignment of projected images becomes very small and is hard to meet during presentations due to thermal induced movements in the mechanical and optical parts and vibrations from the audio system. In other applications like temporary projection set-ups, home cinemas etc., alignment of double stacked projectors may be difficult to maintain even when working at much lower resolutions.
“Double stacking” of projectors, i.e. overlaying the images of two projectors projecting the same image, is a well known way to increase brightness. However, it is also well known that traditional double stacking requires high maintenance of the alignment of the projectors to maintain image quality.
In 4K projection, traditional double stacking is not considered an option, because it would be impossible to keep the sharpness and detail on par with that of a single 4K projector throughout a presentation. This is unfortunate for giant screen theatres, because while 4K projectors lend themselves well to giant screens in terms of resolution, available projectors generally do not have enough light for giant screens, so stacking would seem desirable to double the light output.